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Tuesday, July 25, 2006

A study of netted songbirds in upstate New York has revealed alarmingly high rates of mercury poisoning. Mercury was found in the blood of 178 bird species, with the highest being in wood thrushes. Until the recent studies on landbirds, most of the concern about mercury pollution was focused on fish and their predators. Now we need to worry about land-based sources of the toxin also.

Dr. Evers’s work suggests that when mercury falls on land, it is absorbed by soil and by fallen leaves that are consumed by worms and insects. Songbirds then feed on the bugs, absorbing the mercury.

While all the birds he tested last year had mercury in their blood, wood thrushes had the most, Dr. Evers said, an average of 0.1 parts per million. That is below the federal safe standard for fish (0.3 p.p.m.) but high enough to affect the birds’ reproductive cycle.

With fewer songbirds to eat potentially harmful insects, the state’s forests would be at greater risk for damage by gypsy moths and other pests, Dr. Evers said.

As the article notes, wood thrushes have been in steep decline, up to 45 percent since the 1960s. Habitat fragmentation has been blamed in the past as the primary culprit. Results from this study suggest that mercury pollution is part of the problem as well.

I am not quite sure how this differs from a story produced last year on the same research. It seems that the National Wildlife Federation may be raising the story's profile again. Another study published last year found high levels of mercury and methymercury in Bicknell's Thrushes and Yellow-rumped Warblers.